1. Field of the Invention
This invention relates to the field of raising and harvesting antler-bearing animals, such as deer and elk.
2. Description of the Related Technology
Antlered animals such as deer and elk are raised on farms in the United States and other countries to harvest the growing antlers. The growing antler, also called the velvet antler, is sold as a food supplement around the world, particularly in Asia.
Pain control during harvesting or cutting of the antler is of concern since the velvet antler has an abundant nerve supply. The two primary nerves innervating the pedicle are the infratrochlear and zygomaticotemporal branches of the ophthalmic division of the trigeminal nerve. Sensory branches of the first cervical nerves innervate the posterior aspect of the pedicle, as is shown schematically in FIG. 1.
Traditional methods of pain control include injections of local anesthetics and electroimmobilization. The local anesthetics used are those commonly used in human and veterinary medicine. A few to several injections are made around the pedicle (the base of the antler) and near the nerves supplying the antler. The local anesthetic provides a nerve block, which prevents the pain information from reaching the brain. The shortcoming of this procedure is that a number of subcuticular injections have to be made in the proximity of the nerves around the pedicle and then a wait of five minutes must be made for the local anesthetic to take full effect. The injections must be given at the base of the large antlers in a technique that is known as a ring block. Precise injections are difficult, however, since the deer and elk are large and frequently move their heads.
A second traditional method, electroimmobilization, involves placing a first electrode on the nose and a second on the tail or in the anus. The electrical stimulation causes all the animal's muscles to contract, thus immobilizing the animal. The shortcomings of this procedure relate to the stress induced in the animal by immobilizing all body muscles, including those related to breathing. Studies show that the animals appear to experience more stress related to the electroimmobilization than to the cutting of the antlers. Also, the level of stimulation is difficult to adjust so that the animal is immobilized but still the animal can breathe. This method is not used on people so there are no studies on people to determine if this method provides pain control.
A new method of controlling pain during the harvesting of antlers is the use of transcutaneous electrical nerve stimulation (TENS). This technique has been used in people to control pain associated with medical and dental treatments as well as with muscles and joints. The mechanism of action of TENS is most likely based on the blocking of pain at the first nucleus or first neural relay junction. This mechanism is based on the experimental finding of Melzack, R. and Wall, P. D., Pain Mechanisms: a new theory, Science, 150: 971-979 (1965). By this mechanism, the electrical stimulation of the sensory nerve fibers works to block pain and prevent the nerve impulses representing pain from reaching the brain. The pain control is most effective when the electrical stimulation is delivered to the area of the pain; this is true for TENS as well as local anesthetics.
When TENS is used today spring clamps are placed at various points on the head. One electrode can be placed on the animal's lip and the other on the ear. Alternatively, one electrode can be placed anterior and the other electrode posterior to the pedicle. Another electrode placement puts one clip on each ear. Then the stimulation is increased slowly over a one to three-minute period until muscle contractions cause the ear to lay down against the neck and/or the eye closes. The antler is then surgically cut and removed. For maximum pain control, the electrodes are repositioned and the unit level of stimulation is increased over one to three minutes before cutting the other antler.
While TENS has proved a viable and effective mechanism for anesthetizing the animals during antler harvesting, the process of attaching and disconnecting the various electrodes is difficult. A need exists for an improved TENS system for applying electrical stimulation to antlered animals that is more effective and more convenient to use than the systems that are presently in use.